It has been known that in order to provide an effective spray apparatus for materials with a high particulate content, it is necessary to provide means for maintaining a continuous circulation of the particulate-laden liquid both during the periods when the liquid is being sprayed and during intermediate periods when the spray is interrupted. A continuous circulation of liquid serves to maintain the particulate material in suspension within the carrier liquid.
Conventional valving arrangements have proven to be unsatisfactory for fluent materials in which the particulate material is highly abrasive.
Merely circulating particulate material in a suspension with a carrier liquid, is not, by itself, an answer to all of the problems encountered in spraying high particulate content fluent material. Large particulate material and solutions having particulate material with a wide range of particle size, such as fibers and other aggregate suspensions, not only plug orifices that are the same size or slightly larger than the large particulates, but these larger particulates also agglomerate in large openings impeding or actually blocking the opening, making it difficult, if not impossible, to use these fluent materials in a spray apparatus.
Another difficulty encountered with large particulate materials in suspension arises because the larger particulates tend to pack in, or agglomerate, in valve seats and other openings in a spray apparatus so that the opening or closing of apertures or valves becomes inefficient or even impossible after a short period of use.
In some instances, even where an effective spray apparatus has been provided which permits the continuous recirculation of fluent materials in order to maintain particulate material in suspension within the carrier liquid, that feature is not necessary for some solutions or suspensions, such as paint and the like which do not contain a significant quantity of particulate material. Continuous recirculation in these cases is inefficient, using substantially more energy and equipment, and subjects the spray apparatus to additional sources of leakage.
Accordingly, it would be of great advantage to the art if a spray apparatus could be convertible between a continuous recirculation device, which maintains particulate material in suspension within the carrier liquid and, in its alternative embodiment, a spray apparatus which provides for direct passage of the fluent material through the apparatus without recirculation.
The size of existing spray apparatus, and particularly existing spray guns, has been found to be a limitation as even larger particulate material is used in the particulate laden carrier liquid. The large sized particulate material has been found to require orifices or openings which are too large for conventional spray guns. It would be a great advance in the art if a valving arrangement could be provided which would permit the use of conventional sized spray guns while accommodating larger particulate material in suspension within the carrier liquid.